When a multipage job has only some pages in color, printing the entire job across the color pipeline implies additional costs that, in volume, may be significant. One known solution to minimize those costs are to send only the pages that contain color elements across the color pipeline and use the black and white path for the rest. However, this requires detecting in advance which pages can be printed using black ink only.
Unfortunately, detection of which pages can be printed by a black ink is not trivial. Elements in the image to be printed, e.g. elements within the PDF document, can be stored in a multitude of color models and color spaces. Gray elements in an image, for example contained within a PDF document, can be encoded in a multitude of ways, depending on the color model they use.